Unicast to Multicast Conversion

ABSTRACT

A method for unicast packet conversion whereby a unicast packet is received at a receiving node followed by a determination as to whether the destination address is identified in the packet. If the address is identified, then the unicast packets are converted to a multicast packet and forwarded to a connected station. If a destination network address is not identified, then the packet is forwarded to the connected station.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation in part and claims the priority benefit of U.S. patent application Ser. No. 12/718,987 entitled “MAC Based Mapping in IP Based Communications,” which was filed Mar. 7, 2010; U.S. patent application Ser. No. 12/718,987 is a continuation and claims the priority benefit of U.S. patent application Ser. No. 11/985,865 entitled “Improved Communications Throughput with Unicast Packet Transmission Alternative,” which was filed Nov. 16, 2007; U.S. patent application Ser. No. 11/985,865 is a division and claims the priority benefit of U.S. patent application Ser. No. 11/232,196 entitled “Systems and Methods for Improved Data Throughput in Communications Networks” filed Sep. 20, 2005 and now U.S. Pat. No. 7,505,447; U.S. patent application Ser. No. 11/232,196 claims the priority benefit of U.S. provisional application No. 60/625,331 filed Nov. 5, 2004. The disclosure of each of the aforementioned application is incorporated herein by reference.

BACKGROUND

1. Field of the Invention

The present invention relates generally to communications networks and more particularly to systems and methods for increased data throughput in communications networks.

2. Description of the Related Art

Demand for multimedia applications, including audio and video data, is rapidly increasing. Some of the more popular uses of multimedia are real-time interactive applications, such as video and audio streaming, Internet Protocol TV (IPTV), transmission of lectures or speeches to a remote audience, and animated simulations. Even when data compression is used, multimedia applications require large amounts of bandwidth.

In an Institute of Electrical and Electronics Engineers (IEEE 802.11) wireless local area network (LAN), broadcast, or multicast packet transmission enables bandwidth-intensive multimedia applications to simultaneously transmit audio and video data packets to each receiving node associated with a group of the wireless LAN. Broadcast packets are transmitted to all receiving nodes of the wireless LAN, whereas multicast packets are transmitted to two or more, but fewer than all, of the receiving nodes of the wireless LAN.

In the wireless LAN, a source node may transmit (e.g., via Ethernet) multicast packets to a multicast-enabled access point, and the access point sends the multicast packets via wireless transmission to destination receiving nodes that have identified themselves as part of the multicast group. The access point of the wireless LAN may also support unicast packet transmission.

For unicast transmission in the wireless LAN, the access point transmits one or more unicast packets to the receiving node identified by an intended destination address included in the unicast packets. After receiving the unicast packet, the receiving node transmits (approximately 9 μs later) an 802.11 acknowledgement (ACK) packet back to the access point. The 802.11 ACK mechanism provides reliable data transmission in the typically highly interfered 802.11 wireless network by confirming to the access point that the unicast packet was received.

A limitation with transmitting multicast packets in the wireless LAN is that the 802.11 ACK does not provide a reliable mechanism for ensuring that the receiving nodes actually received the multicast packets. For example, if the 802.11 access point were to transmit one or more multicast packets to a number of receiving nodes, and each of the receiving nodes were to respond essentially simultaneously with 802.11 ACK packets, the multiple ACK packets received by the access point would constitute ‘noise’ during the period of the multiple simultaneous 802.11 ACKs. To the access point, these multiple simultaneous 802.11 ACKs are undecipherable. This condition may be referred to as the ‘multiple ACK problem.’

Another limitation with transmitting multicast packets is that the wireless LAN may be limited in the bandwidth used for multicast packets. Because of the multiple ACK problem, the IEEE 802.11 specification for multicast dictates that transmission of multicast packets occur at a minimum allowable physical data rate. Because the receiving nodes may be at various distances from the source of the transmission and may experience various interference levels, transmitting at the minimum allowable physical data rate improves the probability of reception of the multicast packets by each receiving node. For example, an 802.11 access point transmits multicast packets at a minimum allowable physical data rate of 1 Mbps for 802.11b and 6 Mbps for 802.11a. The receiving nodes do not transmit 802.11 ACK packets to verify reception of the multicast packets. Thus, without the 802.11 ACK mechanism, there is no verification of reception of the multicast packets.

Further, transmitting at the minimum allowable physical data rate under-utilizes available bandwidth in the wireless LAN, which otherwise is capable of supporting much higher data rates. In addition, transmitting at the minimum allowable physical data rate may make the wireless LAN unsuitable for applications that require high rate communication, such as multimedia applications.

SUMMARY OF THE INVENTION

In a first claimed embodiment, a method for unicast packet conversion is claimed. Through the method, a unicast packet is received at a receiving node followed by a determination as to whether the destination address is identified in the packet. If the address is identified, then the unicast packets are converted to a multicast packet and forwarded to a connected station. If a destination network address is not identified, then the packet is forwarded to the connected station.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a block diagram of a system for multicast transmission in a wireless local area network.

FIG. 2 illustrates an exemplary method for multicast or unicast transmission in the wireless local area network of FIG. 1.

FIG. 3 illustrates an exemplary timing diagram illustrating conversion of multicast packets into unicast packets as described with respect to FIGS. 1 and 2.

FIG. 4 illustrates an exemplary method for receipt and subsequent conversion of a unicast packet transmitted in accordance with the method illustrated in FIG. 2.

DETAILED DESCRIPTION

The systems and methods disclosed herein enable data throughput in communication networks greater than that which is provided in the prior art. For example, the system and method disclosed herein support bandwidth-intensive multimedia applications over wireless LANs. In the disclosure, nodes of a communication network may be referred to as a host, a source, a destination, a node, a receiving node, an access point, and a station. The references should not be considered in a limiting sense, as it is understood that the present invention is in no way limited to only the embodiments illustrated. For example, a “receiving node” is in no way limited to the function of receiving only. Additionally, the term group packet includes a multicast packet, a broadcast packet, and any packet whose destination address indicates one or more addresses and/or nodes of the communications network.

According to one embodiment, a wireless local area network (LAN) comprises an access point configured to receive a multicast or broadcast packet from a source. The multicast or broadcast packet is addressed to a group comprising one or more nodes of a communications network (e.g., stations associated with the access point of the wireless LAN). The access point determines whether to convert the multicast or broadcast packet into one or more unicast packets for sequential transmission to the one or more nodes or whether to transmit the multicast or broadcast packet to the group. If the access point transmits the multicast or broadcast packet without conversion, the access point may determine a lowest common denominator data rate based on data rates for transmitting multicast or broadcast packets to the one or more nodes and transmits the multicast or broadcast packet to the group at the lowest common denominator rate.

FIG. 1 illustrates a block diagram of a system 100 for multicast packet transmission in a wireless local area network, in accordance with one embodiment of the present invention. The system 100 comprises a source node 110, a network link 115, an access point 120, receiving nodes 130, 140, and 150, wireless links 135, 145, and 155, and a group 160 comprising two or more of the receiving nodes (e.g., the receiving nodes 130 and 140). The source node 110 is configured to communicate with the access point 120 over the network link 115. The access point 120 is configured to communicate with the receiving nodes 130-150 over the wireless links 135-155 that form the wireless LAN.

The source node 110 is any device capable of network communication including unicast or multicast packet transmission with the access point 120 over the network link 115. The source node 110 may comprise, for example, a personal computer, a server, a network attached storage device, or a network video distribution device. The source node 110 may support networking protocols such as Transmission Control Protocol/Internet Protocol (TCP/IP), User Datagram Protocol (UDP/IP), and/or Internet Group Management Protocol (IGMP), and may support unicast, multicast, and/or broadcast packet transmission of network data.

The source node 110 is configured to transmit one or more group packets addressed to the group 160 (e.g., one or more multicast or broadcast packets) over the network link 115. The network link 115 may be a wired or wireless network link. In one embodiment, the network link 115 comprises a UDP/IP connection. In one example, the source node 110 comprises an IPTV video server (not shown) that transmits the multicast packets, providing a remote video stream to the group 160 through the access point 120. Although discussed in regard to multicast transmission, the group packets may comprise a packet whose destination address specifies all (i.e., broadcast), or less than all (i.e., multicast) of the receiving nodes 130-150.

The receiving nodes 130-150 each comprise any device capable of receiving network communication from the source node 110 through the access point 120 over the wireless links 135-155. The receiving nodes 130-150 may comprise devices such as personal computers, PDAs, cell phones, and/or internet enabled televisions. In one example, the receiving nodes 130-140 of the group 160 may comprise TV set-top boxes configured to receive a video stream provided by the IPTV server at the source node 110 to the group 160. Although described as the source node 110 and the receiving nodes 130-150, it should be noted that the source node 110 may also be the destination node of a data packet as well as the receiving nodes 130-150 may also be the source node of a data packet.

As described further herein, the access point 120 is configured to transmit the video stream to the receiving node 130 and the receiving node 140 either simultaneously as a multicast packet, or sequentially as one or more unicast packets to each of the receiving nodes 130 and 140. The access point 120 is virtually any device capable of acting as a bridge in a peer-to-peer connection in the wireless LAN or as a bridge between the network link 115 and the wireless links 135-155. The access point 120 may be configured to convert the multicast packet into one or more unicast packets, as discussed further with respect to FIG. 2. The access point 120 may include a processor, a memory, and additional circuitry that provides or assists in providing the bridge and/or the multicast packet conversion. The access point 120 may use the IEEE 802.11 protocol, such as 802.11a or 802.11b, to communicate with the receiving nodes 130-150. It will be appreciated that the access point 120 may incorporate other wireless protocols, such as 802.11g, 802.16, or Bluetooth.

The access point 120 may support multicast control protocols, such as IGMP, and may be configured as a multicast-enabled router. A multicast control protocol enables the access point 120 to determine from the receiving nodes (e.g., the receiving nodes 130-150) which group(s) (e.g., the group 160) the receiving nodes 130-150 are associated with. Some examples of multicast control protocols are IGMP, Protocol-Independent Multicast (PIM), Real-Time Streaming Protocol (RTSP), Multiprotocol Border Gateway Protocol (MBGP), Multicast Source Discovery Protocol (MSDP), Simple Service Discovery Protocol (SSDP), and Source Specific Multicast (SSM). For example, the receiving node 130 may send a multicast control protocol packet to the access point 120 to change the channel for an IPTV multicast stream received from the source node 110. The multicast control protocol packet informs the access point 120 that the receiving node 130 is interested in receiving group packets for the selected channel.

The access point 120 of some embodiments is further configured to maintain information about “associated nodes.” Associated nodes are devices that have negotiated a wireless communication link (e.g., the wireless link 135) with the access point 120. For example, when the receiving node 130 initially associates with the access point 120 to negotiate the wireless link 135, the receiving node 130 provides a Media Access Control (MAC) or hardware address that uniquely identifies the receiving node 130. The receiving node 130 may also provide a list of allowable physical data rates (e.g., 1 Mbps-54 Mbps) at which it may communicate with the access point 120. The access point 120 may store such information about the associated nodes in memory, for example.

As described further herein, the system 100 improves multicast data throughput in the wireless LAN because the access point 120 of one embodiment is configured to convert the multicast packet addressed to the group 160 into one or more unicast packets addressed to the receiving nodes 130-140. The access point 120 may transmit the one or more unicast packets sequentially to the receiving nodes 130-140 at a higher data rate than the minimum data rate used for 802.11 multicast transmission. Further, the access point 120 of this embodiment would ensure reliable transmission of the converted multicast packet because the access point 120 would be able to service 802.11 ACK packets generated by the receiving nodes 130-140. In some embodiments, the access point 120 may determine not to convert the multicast packet into one or more unicast packets, but instead may transmit the multicast packet to the receiving nodes of the group 160 at a relatively higher data rate than the minimum allowable physical data rate used for 802.11 multicast packet transmission.

FIG. 2 illustrates an exemplary method for multicast or unicast transmission in the wireless local area network of FIG. 1, in accordance with one embodiment of the present invention. The steps of the exemplary method are described as occurring in particular order, but it will be appreciated that certain steps may be rearranged to provide a similar result. The method determines whether to convert a multicast packet into one or more unicast packets or whether to transmit the multicast packet. The method also determines at what rate to transmit the multicast packet and the one or more unicast packets. The method begins with the access point 120 already associated with receiving nodes 130-150.

In step 205, the access point 120 receives a first join request (e.g., a multicast control protocol packet such as an IGMP join request) from the first receiving node (e.g., the receiving node 130) containing a first address for the receiving node 130. The access point 120 uses the join request to correlate the receiving node 130 with the address of the group 160. In IGMP, a multicast client (e.g., the receiving node 130) joins a multicast group (e.g., the group 160) to enable group reception of a multicast traffic stream. When the access point 120 receives the IGMP join request from the receiving node 130, the access point 120 inspects the IGMP packet and determines the required join information.

In this embodiment, the access point 120 does not itself use the IGMP protocol. Regardless, the system 100 takes advantage of the fact that the IGMP join requests from the receiving nodes 130-140 to the source node 110 pass through the access point 120. The access point 120 “sniffs” or samples the IGMP join requests to map the hardware (MAC) address of the receiving nodes 130 and 140 with the address of the group 160. In some embodiments, the access point 120 “speaks” the IGMP protocol. The access point 120 may map the IP addresses (instead of the MAC addresses) of the receiving nodes 130 and 140 to the address of the group 160.

In the alternative to sniffing or speaking IGMP or other control protocols from the receiving nodes 130-150, the access point 120 may maintain a map that contains the hardware addresses of all or a subset of the receiving nodes 130-150 that are associated with the access point 120. The access point 120 may use the map to query the receiving nodes 130-150 to determine which of the receiving nodes 130-150 are interested in receiving multicast traffic addressed to the group 160. These maps of MAC addresses or IP addresses allow the access point 120 to convert the multicast packet received from the source node 110 and addressed to the group 160 into one or more unicast packets addressed to the receiving nodes 130-140 of the group 160.

In step 210, the access point 120 maps the first address of the receiving node 130 from the IGMP packet to the address of the group 160. In step 215, the access point 120 receives a second join request (e.g., a second IGMP join request) from a second receiving node (e.g., the receiving node 140). In step 220, the access point 120 maps a second address of the receiving node 140 to the address of the group 160.

In step 225, the access point 120 receives the multicast packet addressed to the group 160. In step 230, the access point 120 determines a first data rate (e.g., 54 Mbps) by which the access point 120 may reliably transmit (e.g., including the 802.11 ACK mechanism) one or more unicast packets to the receiving node 130. In step 235, the access point 120 determines a second data rate (e.g., 24 Mbps) by which the access point 120 may reliably transmit one or more unicast packets to the receiving node 140. Although not depicted, in some embodiments the access point 120 may determine additional (e.g., a third or more) data rates by which the access point 120 may reliably transmit one or more unicast packets to a third receiving node (e.g., the receiving node 150 which would be part of the group 160).

In step 240, the access point 120 determines an effective unicast rate. As discussed further with respect to FIG. 3, the effective unicast rate corresponds to a combined rate for converting the multicast packet into one or more unicast packets and sending the one or more unicast packets to the receiving nodes 130 and 140 of the group 160 at the first and second (and third . . . ) data rates. The effective unicast rate depends on the total number of bits included in the unicast packets, including additional data packet overhead (e.g., additional bits in the unicast packet as compared to the multicast packet). The effective unicast rate also depends on computational time associated with converting the multicast packet into one or more unicast packets. The effective unicast rate is further based on the duration for reception and processing of ACK packets from the receiving nodes of the group 160. Further, the effective unicast rate is based on the number of receiving nodes in the group 160, because each additional receiving node in the group 160 proportionally lowers the effective unicast rate. One method for determining the effective unicast rate is presented in co-pending U.S. patent application entitled “System and Method for Transmission Parameter Control for an Antenna Apparatus with Selectable Elements,” the subject matter of which is hereby incorporated by reference.

As described further, rather than converting the multicast packet to unicast packets, the access point may transmit at a “lowest common denominator rate” to the group 160. For example, the lowest common denominator rate may be higher than the effective unicast rate, particularly with a large number of receiving nodes in the group 160 each receiving at a relatively high rate. For example, the group 160 may comprise the receiving nodes 130, 140, and 150. The receiving node 130 may receive packets at a physical data rate of 54 Mbps, the receiving node 140 may receive packets at a physical data rate of 54 Mbps, and the receiving node 150 may receive packets at a physical data rate of 54 Mbps. The lowest common denominator rate for this example is 54 Mbps, which may be higher than the effective unicast rate. In step 245, the access point 120 determines the lowest common denominator rate (LCDR) for transmitting the multicast packet simultaneously to the receiving nodes of the group 160.

In steps 250-295, the access point 120 determines whether to transmit unicast or multicast packets, and at what rate to transmit the unicast or multicast packets. Specifically, in steps 250-275, the access point 120 may determine to convert the multicast packet into one or more first unicast packets addressed to the receiving node 130 and one or more second unicast packet addressed to the receiving node 140 for transmission. Alternatively, in steps 285-295, the access point 120 may determine to transmit the multicast packet simultaneously to the receiving nodes 130-140 of the group 160 and not convert the multicast packet into unicast packets. Further, in steps 285-295 the access point 120 determines whether to transmit at the lowest common denominator rate if the lowest common denominator rate is higher than the minimum allowable physical data rate.

In step 250, the access point 120 determines if the effective unicast rate exceeds the lowest common denominator rate. For example, in an 802.11a wireless LAN with the receiving nodes 130, 140, and 150 in the group 160, the first data rate may be 54 Mbps, the second data rate may be 6 Mbps, and the third data rate may be 54 Mbps. The effective unicast rate, given the number of data bits in the unicast packets, packet overhead, conversion processing time, and the like may be 11.5 Mbps, for example. Accordingly, the effective unicast rate of 11.5 Mbps exceeds the lowest common denominator rate of 6 Mbps (i.e., the minimum allowable physical data rate for 802.11a), so the access point 120 will convert the multicast packet into one or more unicast packets in steps 255-275.

In step 255, the access point 120 converts the multicast packet to a first unicast packet addressed to the receiving node 130. In step 260, the access point 120 transmits the first unicast packet to the receiving node 130 at the first data rate. After transmission of the first unicast packet, in step 265 the access point 120 may delay for a predetermined delay period before converting the multicast packet into a second unicast packet and transmitting the second unicast packet to the receiving node 140 in steps 270-275. The delay period is computed to allow the receiving node 130 sufficient time to generate an 802.11 ACK that the access point 120 may receive to verify reliable transmission and reception of the first unicast packet. The access point 120 may compute the delay period based on several factors. For example, the access point 120 may compute the delay based on computational time needed by the access point 120 to convert the multicast packet into the first unicast packet. The delay may include data packet overhead (e.g., additional bits in the first unicast packet that reduce the first data rate to a relatively lower “user” data rate). Further, the access point 120 may retransmit the first unicast packet to the receiving node 130 if the access point 120 does not receive the 802.11 ACK from the receiving node 130 for the first unicast packet, adding to the delay.

In step 270, the access point 120 converts the multicast packet from the source node 110 into a second unicast packet addressed to the receiving node 140. In step 275, the access point 120 transmits the second unicast packet at the second data rate to the receiving node 140. In similar fashion to the method described above with respect to steps 260-265 for the first unicast packet, the access point 120 awaits an 802.11 ACK from the receiving node 140 to ensure reliable transmission and reception of the second unicast packet. The access point 120 may retransmit the second unicast packet to the receiving node 140 if the access point 120 does not receive the 802.11 ACK from the receiving node 140. Although not depicted, the steps 265 to 275 may be repeated for additional (e.g., third . . . ) receiving nodes in the group 160.

Optionally, the access point 120 may determine in step 260 and step 275 whether one of the receiving nodes of the group 160 comprises a multicast data transmitter. For example, if the receiving node 130 acts as the source node 110 for sending the multicast packet through the access point 120 to the receiving nodes 140 and 150 of the group 160, the access point 120 need not retransmit the converted unicast packet back to the receiving node 130. Although sending the unicast packet back to the receiving node 130 is legitimate practice in 802.11, doing so wastes network bandwidth.

At step 250, if the effective unicast rate does not exceed the lowest common denominator rate, the access point 120 may determine not to convert the multicast packet into one or more unicast packets for sequential transmission to each receiving node in the group 160. Accordingly, in step 285, the access point 120 determines whether the LCDR exceeds the minimum allowable data rate. For example, if the receiving node 130 is capable of receiving at 54 Mbps and the receiving node 140 is capable of receiving at 24 Mbps, the LCDR of 24 Mbps exceeds the minimum allowable data rate of 6 Mbps. Accordingly, in step 290 the access point 120 will transmit the multicast packet to the group 160 at the LCDR of 24 Mbps. Alternatively, at step 285 if the receiving node 130 is capable of receiving at 54 Mbps and the receiving node 140 is capable of receiving at only 6 Mbps, for example, the LCDR does not exceed the minimum allowable data rate of 6 Mbps. Accordingly, in step 295, the access point 120 will transmit the multicast packet to the group 160 at the minimum allowable data rate of 6 Mbps.

The methods described with respect to FIG. 2 advantageously achieve higher data throughput than traditional multicast transmission, by converting multicast packets in the access point 120 into one or more unicast packets that may be transmitted sequentially to each receiving node of the group 160 at a relatively higher data rate. Further, converting the multicast packet into unicast packets affords higher data transmission reliability because the unicast packets are verified by ACK responses from each receiving node of the group 160. Additionally, if the access point 120 determines not to convert multicast packets into unicast packets, the access point 120 may transmit the multicast packet at the lowest common denominator rate, which is a higher physical data rate than the minimum allowable physical data rate defined in the IEEE 802.11 standard.

Although FIGS. 1 and 2 generally describe multicast data flow from the source node 110 to the group 160 (i.e., left to right in FIG. 1), the methods described with respect to FIG. 2 are applicable to multicast control protocol packets that flow in the opposite direction (e.g., from right to left in FIG. 1). For example, the system 100 may include a source node (e.g., the receiving node 130) configured to transmit a group packet to a destination node (e.g., the access point 120). The receiving node 130 sends a multicast control protocol packet, such as an IGMP join request, over the wireless link 135 to the access point 120 to join a group (e.g., group 160) receiving an IPTV multimedia multicast stream. To provide more effective use of the available bandwidth of the wireless link 135, and to provide reliable transmission of the multicast control protocol packet, the receiving node 135 may convert the multicast control protocol packet to one or more unicast packets for transmission to and acknowledgement by the access point 120.

In one example, the receiving node 130 determines a first data rate for transmitting the group packet and determines a second data rate based upon converting the group packet to a unicast packet addressed to the access point 120. The receiving node 130 transmits the unicast packet at the second data rate through the wireless link 135 to the access point 120 if the first data rate for transmitting the group packet is less than the second data rate for transmitting the unicast packet. As discussed herein, the receiving node 130 transmits the unicast packet at a higher physical data rate than specified for multicast transmission. Upon receipt of the unicast packet, the access point 120 sends an ACK to acknowledge receipt of the unicast packet.

If the first data rate for transmitting the group packet is greater than the second data rate for transmitting the unicast packet, the receiving node 130 may transmit the group packet through the wireless link 135. As previously discussed, the receiving node 130 may transmit the group packet at the lowest common denominator rate. The access point 120 then receives the group packet and processes the multicast control protocol packet. Therefore, in these embodiments, the receiving node 130 and the access point 120 individually determine whether transmitting the group packet or converting the group packet to one or more unicast packets allows more effective use of the available bandwidth and reliable transmission.

FIG. 3 illustrates an exemplary timing diagram comparing the conversion of the multicast packet into one or more unicast packets, as described in FIGS. 1-2, as compared to multicast packet transmission, in accordance with one embodiment of the present invention. A first time interval 310 indicates the time needed for the access point 120 to convert the multicast packet received from the source node 110 into the first unicast packet and transmit the first unicast packet to the receiving node 130, for example, at 54 Mbps. It will be appreciated that the time interval 310 may vary depending upon at least the first data rate, the number of data bits in the first unicast packet, and the conversion time needed by the access point 120 to convert the multicast packet into the first unicast packet. After the first unicast packet is transmitted to the receiving node 130, an ACK time interval 320 indicates the time needed for the receiving node 130 to return the 802.11 ACK corresponding to the first unicast packet and for the access point 120 to process the 802.11 ACK packet.

Similarly, a second time interval 330 indicates the time needed for the access point 120 to convert the multicast packet received from the source node 110 into the second unicast packet and transmit the second unicast packet to the receiving node 140 at the second data rate, for example, 18 Mbps. A second ACK time interval 340 indicates the time needed for the receiving node 140 to return an 802.11 ACK corresponding to the second unicast packet and for the access point 120 to process the 802.11 ACK packet. In comparison, a multicast time interval 350 indicates the duration for the access point 120 to receive and transmit the multicast packet simultaneously to the receiving nodes 130 and 140 at either the lowest common denominator rate or the minimum allowable physical data rate.

Because the duration of the combined time intervals 310, 320, 330, and 340 is shorter than the duration of the multicast time interval 350, the system and method described herein advantageously achieve a higher data throughput by converting the multicast packet to sequential unicast packets. Further, as the duration of the time intervals 310 and 320 increases because of interference in the wireless links 135 and 145 (FIG. 1) leading to lower first and second data rates, for example, the combined duration of the time intervals 310, 320, 330, and 340 may exceed the multicast time interval 350. In such case, the lowest common denominator rate may provide a higher data rate than the minimum allowable data rate. Another advantage, therefore, is graceful degradation of the overall data transmission rate with changes in the wireless LAN.

FIG. 4 illustrates an exemplary method 400 for receipt and subsequent conversion of a unicast packet transmitted in accordance with the method illustrated in FIG. 2. In some instances, use of the conversion methodology disclosed with respect to FIG. 2 might ‘confuse’ some receiving nodes. A receiving node, in accordance with most IEEE specifications, will handle two MAC addresses. The first such address is an address that is assigned to the node, usually during the manufacturing process. The second such address is a broadcast address that is generally understood to be a MAC address of all 0xFFs.

Specifications tend to be less clear, however, when dealing with multicast addresses. It is typical for a receiving box to use a MAC layer filter mechanism to allow only certain or universally known multicast MAC addresses to be handled by a receiving node. By filtering out unwanted multicast traffic, only the upper layers need be involved in packet conversion.

In certain instances of a receiving node, there exist implementation layers that correspond to the various architectural layers such as the OSI-7 layer model and that allow a layer of logic to have specialized handling of its respective architectural layer. For example, the MAC-layer would be ‘knowledgeable’ about the MAC portion, such as destination MAC addresses, but lack information as to other layer, such as layer-3 or IP headers. The decision of the MAC-layer can be a binary one—drop a packet or pass that packet up to the next layer.

In an alternative embodiment of the present application, the respective assigned MAC address of a node may be used as the destination MAC address of the packet. In such an embodiment, the layer-3 and above information is left unchanged meaning that the MAC-layer processing in the receiving node will recognize its packets and send them up to the next layer for processing.

As a counter to the implementation layer referenced above, some nodes will be constructed such that the node will recognize its own assigned MAC address and the broadcast MAC address and pass matching packets to the next higher layer. However, in the case of a multicast MAC filter match, the packets are passed to a multicast packet handler in the next higher layer. In the interest of a cheaper and less expensive receiving node, logic may be implemented in the MAC layer that is aware of the layer-3 header such that there exist two connections to the MAC layer with the layer 3: one for management/configuration and one for video. The first connection uses the node's assigned MAC address and the second uses a multicast address.

The method 400 of FIG. 4 thus operates to receive a unicast packet at a receiving node in step 410. A determination is made at step 420 as to whether the destination address is identified in the packet. If the address is identified, then the unicast packets are converted to a multicast packets at step 430 followed by forwarding of the packet to a connected station at step 440. The conversion methodology may differ depending on a particular network, but is based on the network address. If the destination network address is not identified in step 420, then the methodology proceeds directly to step 440 where the unicast packet is forwarded to the connected station.

The embodiments discussed herein are illustrative of one example of the present invention. As these embodiments of the present invention are described with reference to illustrations, various modifications or adaptations of the methods and/or specific structures described may become apparent to those skilled in the art. All such modifications, adaptations, or variations that rely upon the teachings of the present invention, and through which these teachings have advanced the art, are considered to be within the scope of the present invention. Hence, these descriptions and drawings should not be considered in a limiting sense, as it is understood that the present invention is in no way limited to only the embodiments illustrated. The scope of the invention should, therefore, be determined not with reference to the above description, but instead should be determined with reference to the appended claims along with their full scope of equivalents. 

1. A transmission method, comprising: receiving a unicast packet at a receiving node; determining that the destination address is identified in the packet; converting the unicast packet to a multicast packet based on a network address; and forwarding the converted packet to a connected station.
 2. A non-transitory computer readable storage medium having embodied thereon a program, the program being executable by a processor to perform a transmission method, the method comprising: receiving a unicast packet; determining that the destination address is identified in the packet; converting the unicast packet to a multicast packet based on a network address; and forwarding the converted packet to a connected station. 